Nicotinic acid has been used for many years in the treatment of hyperlipidemia. This compound has long been known to exhibit the beneficial effects of reducing total cholesterol, low density lipoproteins or "LDL cholesterol", triglycerides and apolipoprotein a (Lp(a)) in the human body, while increasing desirable high density lipoproteins or "HDL cholesterol".
Nicotinic acid has normally been administered three times per day after meals. This dosing regimen is known to provide a very beneficial effect on blood lipids as discussed in Knopp et al; "Contrasting Effects of Unmodified and Time-Release Forms of Niacin on Lipoproteins in Hyperlipidemic Subjects: Clues to Mechanism of Action of Niacin"; Metabolism 34/7, 1985, page 647. The chief advantage of this profile is the ability of nicotinic acid to decrease total cholesterol, LDL cholesterol, triglycerides and Lp (a) while increasing HDL particles. While such a regimen does produce beneficial effects, cutaneous flushing and the like still often occurs in the hyperlipidemics to whom the compound is administered.
In order to avoid or reduce the cutaneous flushing a number of materials have been suggested for administration with an effective antihyperlipidemic amount of nicotinic acid, including guar gum in U.S. Pat. No. 4,965,252, and mineral salts as disclosed in U.S. Pat. No. 5,023,245; or inorganic magnesium salts as reported in U.S. Pat. No. 4,911,917. These materials have been shown to the cutaneous flushing of the side effects commonly associated with nicotinic acid treatment.
Another method of avoiding or reducing the side effects associated with immediate release niacin is the use of sustained release formulations. Sustained release formulations are designed to slowly release the compound from the tablet or capsule. The slow drug release reduces and prolongs blood levels of drug and thus minimizes the side effects. Sustained release formulations of niacin have been developed, such as Nicobid.TM. capsules (Rhone-Poulenc Rorer), Endur-acin.TM. (Innovite Corporation) and U.S. Pat. No. 5,126,145 which describes a sustained release niacin formulation containing two different types of hydroxypropyl methylcellulose and a hydrophobic component.
Studies in hyperlipidemic patients have been conducted with a number of sustained release niacin products. These studies have demonstrated that the sustained release products do not have the same advantageous lipid altering effects as immediate release niacin, and in fact often have a worse side effect profile compared to the immediate release product. The major disadvantage of the sustained release formulations, as can be seen in Knopp et al., 1985, is the significantly lower reduction in triglycerides (-2% for the sustained release versus -38% for the immediate release) and lower increase in HDL cholesterol, represented as HDL.sub.2 particles which are known by the art to be most beneficial, (-5% for the sustained release versus +37% for the immediate release).
Additionally, sustained release niacin formulations have been noted as causing greater incidences of liver toxicity as described in Henken et al (Am J Med 91:1991 1991) and Dalton et al (Am J Med 93: 102 1992). There is also great concern regarding the potential of these formulations in disrupting glucose metabolism and uric acid levels.
In a recent edition of the JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION (JAMA), an article appeared which presented research results investigating the liver toxicity problems associated with a sustained release form of nicotinic acid. "A Comparison of the Efficacy and Toxic Effects of Sustained- vs Immediate-Release Niacin in Hypercholesterolemic Patients", McKenney et al., JAMA, Vol. 271, No. 9, Mar. 2, 1994, page 672. The article presented a study of twenty-three patients. Of that number 18 or 78 percent were forced to withdraw because liver function tests (LFTs) increased indicating potential liver damage. The conclusion of the authors of that article was that the sustained release form of niacin "should be restricted from use."
A similar conclusion was reached in an article authored by representatives of the Food and Drug Administration and entitled "Hepatic Toxicity of Unmodified and Time-Release Preparations of Niacin", Rader, et al., THE AMERICAN JOURNAL OF MEDICINE, Vol. 92, January 1992, page 77. Because of these studies and similar conclusions drawn by other heath care professionals, the sustained release forms of niacin have experienced limited utilization.
Therefore, it can be seen from the scientific literature that there is a need for development of a sustained release niacin formulation and a method of delivering said formulation which would provide hyperlipidemic patients with "balanced lipid alteration", i.e. reductions in total cholesterol, LDL cholesterol, triglycerides and Lp(a) as well as increases in HDL cholesterol with an acceptable safety profile, especially as regards liver toxicity and effects on glucose metabolism and uric acid levels.